Conventionally, there is proposed a multicarrier communication system that combines a packet obtained at initial transmission with a retransmitted packet to decode, thereby improving an error rate characteristic caused at a decoding time on a receiving side. Then, conventionally, for the purpose of improving the throughput of data, various kinds of contrivances have been proposed to achieve a desired error rate with a small number of retransmissions.
Particularly, in the multicarrier communication system, a reception level differs for each subcarrier because of frequency-selective fading. Accordingly, the reception level of a signal on which a subcarrier with a certain frequency is superimposed becomes high but the reception level of the signal on which another subcarrier is superimposed becomes low. As a result, the error rate of the signal on which a subcarrier with a low reception level does not easily achieve a desired value, so that the number of retransmissions increases.
In consideration of this point, there are methods disclosed in Unexamined Japanese Patent Publication Nos. 2001-60934 and 2000-269929. In these methods, an interleave pattern is changed for each retransmission to vary a subcarrier that locates a symbol for each retransmission. As a result, the signal level of each symbol can be unified at a packet combining time to make it possible to improve the error rate characteristic.
By the way, according to the conventionally proposed method that changes the interleave pattern for each retransmission, since variations in transmission symbols can be, indeed, made greater by interleave processing, a symbol with an extremely low error rate can be reduced to enable to improve the throughput of data effectively.
However, in recent years, it has been demanded that a large capacity of data such as image data is transmitted at high speed, and in order to achieve this, it is needed to further improve the error rate characteristic to reduce the number of retransmission times, thereby much more improving the throughput.